1. Field of the Invention
The present invention relates to a cylindrical commutator that is used for a compact motor, and a method of manufacturing the same.
2. Description of the Related Art
A cylindrical commutator that is used for a compact electric motor comprises a plurality of segments having hooks at one side for line connection, which are fixed cylindrically in a mold resin. Folded anchors are fixing the segments to the mold resin are provided at both ends of the segments, and are embedded into the mold resin.
In the above structure, the segments are fixed to the mold resin with the anchors at both ends. A portion near the center in the axial direction of the segments is not engaged with the mold resin. There are some problems such that the portion near the centers of the segments becomes buoyant above the mold resin during a high speed rotation.
U.S. Pat. No. 5,204,574 discloses a cylindrical commutator having anchors also provided at the center portion in the axial direction of the segments. The production process is such; deep grooves and shallow recesses are formed mutually on planar base metal, lands between the grooves and the recesses are prepared by cutting in a V-shape with wedge, thereby to form anchors. As the segments have anchors substantially over their total length, the segments can be connected more certainly in comparison with the case of the said conventional cylindrical commutator.
The above technique has a drawback in that it is possible to form only very low anchors, as the height of the anchors formed is restricted by the height of the ridge. Further, as the cylindrical shape is formed by bending the base metal having the grooves and the recesses, there arise distortions on the cylindrical surface. This leads to a loss of forming precision.
It is an object of the present invention to provide a cylindrical commutator that can be fixedly held using a mold resin and in a high forming precision.
According to the present invention, a commutator is formed as follows. On the internal surface of a base metal cylinder equipped with the plurality of hooks at one end, cuts are formed in a circumferential direction corresponding to each of a plurality of hooks. The cuts are opened to an internal direction to form projections. The cylinder is set to a molding die, and the prepared projections are embedded into a mold resin. On the external peripheral surface of the mold resin, slits are processed at equal intervals in a circumferential direction, and the hooks and the prepared projections are divided for each segment.